After a week of growing in the garden The fungus in drying over a radiator tonight prior to being posted to Key Gardens for examination. The central picture above shows the fungus in situ with the soil cut away to show its position in the hole. It was deeper than I thought.

You can see several small growths near the bottom right, they are magnified in the right-hand image. I saw these last week and they do not appear to have grown at all since then. The left-hand image shows the base of the stem (stipe) and the white mass of mycelial strands that 'blend' into the soil. They did not seem to be in contact with any particular object.